Device for rendering visible invisible rays



May 16, 1939. H. COANDA DEVICE FOR RENDERING VISIBLE INVISIBLE RAYS Filed June 5, i936 INVENTOR whM M m'ms- Patented Ma 16, 1939 ncvlca FIOR RENDER'ING VISIBLE NVISIBLE mars Henri Chanda, Clichy,

cit Anonyme of France Application June In Ge 3 Claims.

It is a known fact that, among theexlsting waves of various lengths, the so-called infra-red rays are next to the visibleor-light rays but are tion.

iii in through an optical system of lamp h; varies inversely not directly active on the optic nerve because the frequency of the undulation is not suflicient for exciting the optic nervous centers.

This invention relates to a device for rendering visible such rays as are called more, particularly, iectuating of so-called indirect vision of surfaces invisible", and

and/or objects emitting rays which pertain to the infra-red spectrum. More generally, this invention can be applied in cases where rays other than infra-red-ultraviolet rays, for instance--- are to be transformed into visible rays or, alternatively, in cases of the conversion of visible rays into invisible ones, for instance incases where it is desirable to impress actinic rays on a photographic plate after having changed the frequency oi'the rays emitted by the object to be detectedand having but a low actinic power.

A preferred embodiment of the present invention 'willbe hereinafter described, with reference to the accompanying drawing, given merelybyway of example, and inwh'ich: the drawing is a diagrammatic view of this embodiment of the invendiment of my invention, I form, I), a first image of the object a on a screen 0, which image is, or may be, invisible. This image is reproduced on a second screen i, in a visibiemanner, through cooperation with an illuminating lamp h. This lamp is mounted in an electric circuit including a source of current, constituted by battery I, or the equivalent. I The electric circuit further includes, mounted in shunt with said lamp h, a photo-=- electric cell c, hereinaftercalled (pilot cel of a well lmown type, such that an increase in illumi- Iin this emb nation falling upon; said cell decreases the resist creases the flow of current through the branch containing-lamp h and therefore increases the 1.5111011 supplied by said. lamp. in other words, the intensity of illumination of pilot cell c by the light rays dropping thereon from the direction of object a.- by the elements of screen c, determine the amounts of light that are allowed to pass from lamp h to the corresponding elemental areas of but not exclusively, the ef-- with the illumination Means, controlled Brevets et'Proa, corporation 3, 1936, Serial'No. 83,348 rmany June 1,1935

screen i, so as to reproduce the image projected in an invisible manner on the first screen 0.

These means may be of, any suitable type. For instance, in the example illustrated by the drawing, screen consists of the juxtaposition of a .5 multiplicity of photo-electric" cells 0'. As for screen i, it may consist of an ordinarytranslucent screen. Between the lamp h and theelemental areas of said screen i, I provide oscillating screens 7' mounted in anoscillating manner such as that 10 used for the mirrors of galvanometers or oscillographs and the area of which is of a non-uniform transparency varying over itssurface according to a regular law, ranging between total absorption and total free passageof light in such manner the amount of light allowed to pass through each of said screens depends upon the angular position of said screen about its pivoting axis. The pivoting displacements of these screens 7' are controlled through devices is, themselves controlled m by cells ,0, in such manner as to reproduce on screen i an image, of relatively roughtexture, but which fully corresponds to the. image formed on screen 0. For instance, devices k, whichare'inserted in the circuits of the corresponding respective photo-electric cells 0', are analogous to the means for controlling the angular displacements of the mirrors of galvanometers or oscillographs.

In order to improve the image finally obtained,

the image formed on screen 2' is advantageously to projected through an optical system b which reduces its'size on a third screen i on which the image of the invis'ble object a becomes visible for any organ sensitive to the light rays emittedirom source h, for instance the optic nerve of the human eye, photographic emulsions, etc.

A device such as that just above described can be employed for many practical purposes, and especially in navigation, for blind flying, and, in a more general way, in all cases in which a movable body intended to move along a predetermined path of travel, is to avoid invisible and accidental obstacles in the course of its movement, it being of course well understood hat these obstacles emit or are capable of reflecting invisible raysoi at suitable frequencies. By way of example of application of the invention, I may cite the deter.- mination from a distance or obstacles in fog weather, such as stationary obstacles (coast, cliffs, rocks, etc.) or movable obstacles (ice-bergs, wrecks, etc). The device according to the preseht invention can also be applied to aerial navigation, and, especially, to submarine navigation.

While I have, in the above description, disclosed what I deem to be practical and emcient embodi- N that Hil ent invention as prises, in combination,

without departing from the principle or the prescomprehended within the scope of the appended claims.

What Iclaimis: l. A device of the type described, which coinmentioned screen, an electric image of an object onto said screen, a second screen, consisting of a multiplicity of elemental areas corresponding to said elements, respectively, an electric source of light for illuminating said second mentioned screen, an electric circuit for said source of light including a source of current, photo-electric relay means, connected with said circuit, responsive to action of light rays falling thereon from the direction of said object, for controlling the current in said circuit in inverse. relation to the illumination of said relay means, and a plurality of mentioned screen.

3. A device of the typedescribed, which comprises, in combination, a screen consisting of a multiplicity of juxtaposed a second screen,

' of a multiplicity of elemental areas correspondamounts of light in accordance with their resecond mentioned screen, respectively, and means actuated by said photo-electric cells, respectively,

for controlling the angular positions of the cor-' HENRI COANDA. 

